This invention relates to oligomerization and homopolymerization of mono-1-olefin monomers, such as ethylene and propylene, and copolymerization of a mono-1-olefin monomers, such as ethylene and propylene, with at least one higher alpha-olefin comonomer.
It is well known that mono-1-olefins, such as ethylene and propylene, can be oligomerized and polymerized with catalyst systems employing transition metals such as titanium, vanadium, chromium, nickel and/or other metals, either unsupported or on a support such as alumina, silica, titania, and other refractory metals. Supported polymerization catalyst systems frequently are used with a cocatalyst, such as alkyl boron and/or alkyl aluminum compounds. Organometallic catalyst systems, i.e., Ziegler-Natta-type catalyst systems usually are unsupported and frequently are used with a cocatalyst, such as methylaluminoxane.
It is also well-known that, while no oligomer or polymer production process is easy, slurry, or loop, oligomerization or polymerization processes are relatively much more commercially desirable than other oligomerization or polymerization processes. Furthermore, the type of oligomerization or polymerization process used can have an effect on the resultant polymer. For example, higher reactor temperatures can result in low catalyst activity and productivity, as well as a lower molecular weight oligomer or polymer product. Higher reactor pressures also can decrease the amount of desirable branching in the resultant oligomer or polymer.
Most oligomer or polymer products made in slurry processes, especially those oligomer or polymer products made using supported chromium catalyst systems, have a broader molecular weight distribution and, therefore, the oligomer or polymer product is much easier to process into a final product. Oligomers or polymers made by other processes, such as, for example, higher temperature and/or higher pressure solution processes, can produce oligomers or polymers having a narrow molecular weight distribution; these oligomers or polymers can be much more difficult to process into an article of manufacture.
Unfortunately, many homogeneous organometallic catalyst systems have low activity, high consumption of very costly cocatalysts, like supported organoaluminum compounds or methylaluminoxane (MAO), and can produce low molecular weight oligomers or polymers with a narrow molecular weight distribution. Furthermore, even though MAO can be necessary to produce an oligomer or polymer with desired characteristics, an excess of MAO can result in decreased catalyst system activity. Additionally, these types of homogeneous catalyst systems preferably are used only in solution or gas phase oligomerization or polymerization processes.